An automatic door arrangement in a normal operational condition involves a certain amount of friction-induced friction force that resists motion. In case the magnitudes of the friction forces in the door arrangement can be found out by measurement or computationally, the information may be utilized for monitoring the performance and condition of the system.
An automatic door of an elevator consists of a car door moving with the car and operated by a door operator, which comprises a door motor and a door mechanism for moving one or more door leaves in their location horizontally, and landing doors which the car door captures along while on that floor. An elevator door of this kind, which slides automatically on a horizontal rail, is a part on which forces from various directions are exerted and which is in contact, both at its upper and lower edges, with the rail that keeps the door movement in its path. The friction force also resists the movement of the automatic door. The operation of the door may be disturbed, when a sufficient amount of dirt is accumulated on the door slide rail on the threshold of the elevator car. Due to this physical obstacle, the force resisting the motion of the door may become so high that, eventually, a door control system is no longer able to open or close the door.
A large part of elevator failures result from malfunctions in the automatic door of the elevator. Some of the door faults appear in such a way that it becomes heavier for the door motor to move the door. Because the door movement is controlled by a feedback adjuster that corrects changes of this type in the system, as long as there will be enough torque and power in the motor, the operation of the door appears fully normal outwards. Thus, in a feedback system there may be a failure in the making, or the system may originally have been mounted, adjusted or parameterized in a wrong way, but because of the feedback it will not appear outwards for a long time.
Publication EP 1713711 B1 discloses a method for monitoring the condition of an automatic door in a building, which method is based on force balances in a model for the door and on adapting model parameters using an optimization method. As initial data the method requires a current to torque function of a door motor that converts the current of the door to a torque produced by the door, transmission ratio of the door motor and the relating mechanism, by which the torque of the motor is converted to a linear force that moves the door leaves, and a force factor of a spring in a landing door closing device, or, if the closing device is a weight, mass of the weight. In the method, the current of the door motor (system excitation) and acceleration of a door leaf (system response) are to be collected to a buffer of the control system typically at a sampling frequency of 100 Hz during a door operating cycle. To this excitation/response data set are fitted the parameters of the force model such that the model produces as well as possible the same acceleration curve as that in the measured data. After fitting there are known the frictions of the door, the reduced masses of the door and the operational condition of the closing device. As initial data there are required the type of the motor and the current to torque curve of the motor, the type of the closing device, the mass of the weight and the elastic constant of the spring.
Management and parameterization of the required initial data is a challenging task in production and maintenance, requires investment and is sensitive to errors. To insert an optimization algorithm into an embedded elevator control system and to make it function reliably also pose problems, as do the processing and memory capacities required by the algorithm.